Beta particle detection in thin nuclear detectors

ABSTRACT

Detector for beta particles having means for scattering particles back into the detector.

United States Patent Inventors Phillip A. Johnston;

Vincent L. Gelezunas, both ol King of Prussia, Pa

App]. No. 17,403

Filed Mar. 9, 1970 Patented Nov. 16, 1971 Assignee The United States of America as represented by the United States Atomic Energy Commission BETA PARTICLE DETECTION IN THIN NUCLEAR DETECTORS 5 Claims, 1 Drawing Fig.

US. Cl

BACKSCATTERED BETA PARTICLES [51] Int. Cl GOIt 1/24 [50] Field oi Search 250/83, 83.3, 83.3 D; 29/572; 317/235 (27) [56] References Cited UNITED STATES PATENTS 3,124,683 4/1964 Lorson, Jr. 250/68 3,293,435 12/1966 Huth 250/833 R Primary Examiner-James W. Lawrence Assistant ExaminerMorton J. Frome Attorney-Roland A. Anderson ABSTRACT: Detector for beta particles having means for scattering particles back into the detector.

PATENTEB I l97l 3,621,257

BACKSCATTERED BETA PARTICLE S mvm'rore.

PHILLIP A.JCIHNSTOI\I BY VINCENT L.GELEZUNAS /l 'f [WW n? BETA PARTICLE DETECTION IN TIHN NUCLEAR DETECTORS BACKGROUND OF THE INVENTION In the field of physics it is desirable to detect high-energy beta particles. Various means have been proposed and used for this purpose, such as Geiger counters, but as is well known in the art, these and the other gas counters known heretofore have required relatively thick housings for containingthe gas therein, and these housings have absorbed particles that did not ionize the gas. It is additionally advantageous to provide increased beta particle detection efficiency, to reduce the need for large area detectors and complicated electronics, and to provide sensitive beta particle detection for small low-energy beta particle sources.

SUMMARY OF THE INVENTION This invention, which was made in the course of or under a contract with the United States Atomic Energy Commission, provides a means for increasing the detection of beta particles that pass through a detector. More particularly, this invention provides a particular beta radiation source, a semiconductor diode detector having a flat side that is free of a housing, and flat means for scattering back into the detector the beta particles passing through the detector. In one embodiment, the semiconductor diode detector is a flat, wafer-shaped, semiconductor detector having a flat foil adjacent one side thereof for scattering particles into that side of the detector for the detection therein of the scattered particles. In another aspect, this invention also provides for beta particle energy discrimination for various applications With the proper selection and arrangement of the components, as described in more detail hereinafter, the desired beta particle detection and discrimination are provided.

The above and further novel features and objects of this invention will become more apparent from the following detailed description of one embodiment when the same is read in connection with the accompanying drawing and the novel features will be particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention is particular useful in the detection and/or discrimination of beta particles. Thus, as will be understood by one skilled in the art, this invention is useful in a wide variety of applications where such beta particle detection and/or energy discrimination is required. For example, the detector of this invention is useful in'tracer applications, such as in the biomedical field where beta detectors are useful in catheters. Other applications, comprise industrial beta particle detection and measurements, such as are employed in gas leakage measurements. Another such application is in the quality control of the manufacture of light bulbs. Also, this invention is useful in scientific and space applications involving the evaluation of natural, geological, extraterrestrial, or manufactured materials by the use of beta particle detection. In this regard, this invention is useful to techniques such as I(ryptonation" for detection of flaws in solids. Thus, as will be understood in more detail hereinafter this invention is useful with a wide variety of radiation sources, such as Ru Kr, Sr, and radiation sources of a wide variety of sizes and strengths. One description of such sources is provided in Low Energy Radioactivity and Avalanche Detectors," and NYO 3246TA-5,by Johnston Huth and Locker under US. A.E.C. Contract AT( 30-1 3246. However, as will be understood in more detail hereinafter, the wide variety of beta particle sources used in accordance with the embodiments described herein, are limited to those whose beta particles have sufficient energy to pass through the detector.

tor l7 by passing into detector, e.g.' side 23, and

Some beta particles deposit energy in the detector sufficient for detection and some of them do not. However, some beta particles 27 have sufficient energy to pass through the detecface 15 and out side 23, and these can be detected by being deflected back into the detector. To this end, should a foil 29 be placedadjacent to the exit side of the parallel therewith in accordance with this invention, thebeta particles 27 passing through the detector are scatteredby foil 29 on the exit side of the detector 27 so as to pass back into the detector 117 for detection. Thus, by placing the back scatter foil 29 of this invention behind the detector on the exit side 23 of the detector away from beta source It, there are two chances to detect any beta particles incident on the entrance face 15 of the detector closest to the source Ill.

ln the operation of thisinventjon: with Ru beta particles 27 are scattered back into the detector 17 by a thin lead foil 29. A graphof actual results waszmade of the pulse height analyses of the beta particles M from a Ru source 11 that were detected by the detector 17 alone. A 27 graph was made of the actual results of the pulse height analysis of the beta particles detected with the lead foil 29 placed overthe exit side 23 of the detector 17. The result of comparison of the two graphs showed that a 30percent increase in counting efficiency was obtained by the use of die foil 29in an actual test. Also, in this regard, there is provided by the use of foils 29 of various atomic numbers, a simple nonelectronic means of energy discrimination of the beta particles 13 from source 11. Likewise, the distance of foil 17 from detector 17 and the thickness of foil 27 can alternately be used for purposes of control.

In one'application of the described detector system 35 of this invention to rocket thruster, gas leakage detection, a small amount of a Kr source 17 mixed with propellant gas confined on side of detector 117 so as to lead past side l5 as an ambient 37 confined on side 115, will permit measurement leaks as low as 0.001 cmP/hr. by detecting the 667 kev. beta particles from the leaking Kr.

In this regard, the major work on this invention was done with a simple, flat surface, wafer-shaped, diode, semiconductor 37 that was not an avalanche multiplying detector. However, avalanche multiplying detectors 1l7'such as described and shown'in US. Pat. No.3,449,l77, can also be used with this invention. In this regard, in one example, high sensitivity is obtained, and low background and high detection efficiency cles incident on the entrance face of the detector. This invention also provides new and improved nonelectronic means for beta particle energy discrimination.

What is claimed is:

i. Apparatus for detecting and measuring the energy of incident, low-energy beta particles, comprising a low-energy beta source, a diode semiconductor radiation detector for receiving said beta particles, and means for scattering said beta particles back into said detector when they pass through said detector from saidsource, whereby said detector has high efficiency by providing two chances for the detection of said particles passing through said detector.

2. The invention of claim l in which said scattering means, comprises a flat lead foil for scattering back into said detector beta particles passing therethrough from aRu beta particle source.

3. The invention of claim l in which said detector and scattering means have adjacent flat, parallel sides on the exit side of said detector for said particles passing therethrough from said source for measuring gas leaks as low as 0.001 cmP/hr. by detecting 667 kev. beta particles from leaking gas having Kr added thereto.

4. The invention of claim 1 in which said detector, com- 5. The invention of claim 1 in which said means for scatter- Priws a J Internally p y flt avalanche ing beta particles back into said detector is afoil having a zggczltlldiufatsir nlzza rlgsisflagatug fllzgzgg 58:1 predetermined atomic number for s ellectively p 'oviding for parallel with one side of said detector with said detector inter- 5 mm '9' i I i posed between said source and foil. 

1. Apparatus for detecting and measuring the energy of incident, low-energy beta particles, comprising a low-energy beta source, a diode semiconductor radiation detector for receiving said beta particles, and means for scattering said beta particles back into said detector when they pass through said detector from said source, whereby said detector has high efficiency by providing two chances for the detection of said particles passing through said detector.
 2. The invention of claim 1 in which said scattering means, comprises a flat lead foil for scattering back into said detector beta particles passing therethrough from a Ru106 beta particle source.
 3. The invention of claim 1 in which said detector and scattering means have adjacent flat, parallel sides on the exit side of said detector for said particles passing therethrough from said source for measuring gas leaks as low as 0.001 cm.3/hr. by detecting 667 kev. beta particles from leaking gas having Kr85 added thereto.
 4. The invention of claim 1 in which said detector, comprises a PN-junction, diode internally amplifying, avalanche semiconductor detector having flat, uncluttered, opposite sides, and said scattering means is a flat foil spaced from and parallel with one side of said detector with said detector interposed between said source and foil.
 5. The invention of claim 1 in which said means for scattering beta particles back into said detector is a foil having a predetermined atomic number for selectively providing for energy discrimination of the beta particles from said source. 